1. Field of the Inventive Concepts
The inventive concepts disclosed herein are generally directed to medical implants, and more particularly, but not by way of limitation, to an endplate for vertebral implants and to methods of using same.
2. Brief Description of Related Art
The human spinal column, or spine, is highly complex, in that it includes over twenty bones coupled to one another so as to support the body and to house and protect critical elements of the nervous system. In addition, the spine is a highly flexible structure, capable of bending and twisting in multiple directions. The bones and connective tissues of an adult human spine are coupled sequentially to one another by a tri joint complex which consists of an anterior joint between vertebral bodies, and two posterior facet joints. The vertebral bodies of adjacent vertebrae are separated and cushioned by cartilage spacers referred to as intervertebral discs. The vertebral bones of the spine are classified as cervical, thoracic, lumbar, and sacral. The cervical portion of the spine, which includes the upper portion of the spine up to the base of the skull, is the most flexible of all the regions of the spinal column, and includes the first seven vertebrae. The twelve intermediate bones comprise the thoracic vertebrae, and connect to the lower spine which comprises the five lumbar vertebrae. The base of the spine includes the sacral bones (including the coccyx).
A typical human thoracic and lumbar vertebra consists of two essential parts: an anterior (front) segment, which is the vertebral body; and a posterior (back) segment, which is the vertebral arch. The vertebral arch is formed by a pair of pedicles and a pair of laminae, and supports seven processes—four articular, two transverse, and one spinous.
The vertebral body is the largest portion of the vertebrae and is generally cylindrical in shape. Vertebral bodies have upper and lower surfaces, which are generally flat or slightly concave. The surfaces are roughened to allow for the attachment of the intervertebral discs. The vertebral bodies and the intervertebral discs cooperate to provide structural support to the spinal column, with the intervertebral discs cushioning the vertebrae and absorbing and adapting to forces exerted on the vertebral bodies.
In some cases of spinal injuries, the forces exerted on the spinal column are so great, as to cause a partial or complete fracture of one or more of the vertebral bodies, and significant damage to the intervertebral discs surrounding the fractured vertebrae. A vertebral fracture or collapse may also be caused by osteoporosis, infection, tumors, or other diseases.
Regardless of the cause, it is difficult for the damaged vertebral body and intervertebral discs to heal due to the constant forces exerted on the spinal column, or due to the disease progression. Further, due to bulging or displaced damaged vertebrae or intervertebral discs, pressure may be exerted on the spinal cord, or other neural tissues surrounding the damaged vertebrae or intervertebral discs, which may lead to significant pain, neurological damage, and even paralysis in some severe cases.
Surgical procedures called interbody fusion (IBF) and vertebral body replacement (VBR) have been developed to remove the damaged intervertebral discs in the case of IBF and the damaged vertebral body and intervertebral discs in the case if VBR, and to replace them with an implant, such that the height, alignment, and curvature of the spinal column is maintained or is not significantly compromised.
By way of example, VBR is generally performed by locating the damaged vertebral body (e.g., with medical imaging) and accessing it via an appropriate surgical incision. Once the vertebral body is accessible, surgical tools may be used to remove a portion or all of the vertebral body and the two intervertebral discs surrounding the removed vertebral body, such that the lower surface of the vertebral body above and the upper surface of the vertebral body below the removed vertebral body are exposed.
Next, a generally cylindrical implant of appropriate size is selected and inserted in the location of the removed vertebral body. The implant generally has endplates, or another interface, which contact the exposed lower surface of the vertebral body above the removed vertebral body, and the exposed upper surface of the vertebral body below the removed vertebral body. The endplates are configured to engage the implant with the two adjacent vertebral bodies and to keep it in place once implanted.
Some existing VBR implants allow surgeons to adjust the height of the implant to match the original height, alignment, or curvature of the patient's spine, and some implants have a porous hollow body, which allows surgeons to insert a bone graft into the implant. The bone graft may eventually grow through, or around, the implant, and may fuse the two vertebrae that are in contact with the implant over time. One or more supplemental fixation devices, such as stabilizing rods, plates, or bone screws, may be attached to the vertebrae above and below the implant, or even to the implant itself, to provide additional stabilization of the spine while the bone graft is fusing the two vertebrae together. If the VBR implant is a bone-fusion implant, over the next several months the bone graft grows into, or around, the implant to eventually fuse the adjacent vertebral bodies together. If the VBR implant is a non-fusion implant, the supplemental fixation devices and the VBR implant may function to replace the removed vertebral body and discs, and the VBR implant and adjacent vertebrae may not be fused together.
IBF is performed in a manner generally similar to VBR except that only an intervertebral disc is removed such that the lower surface of the vertebral body above and the upper surface of the vertebral body below the removed intervertebral disc are exposed. Next, one or more implants of appropriate size are selected and inserted in the space of the removed disc.
The design, shape, and angle of the vertebral implant endplates that contact the adjacent vertebrae are important in ensuring proper spinal height, alignment, and curvature, and in securely attaching the vertebral implant to adjacent vertebrae, such that the implant does not become dislodged, or otherwise displaced post-implantation.
However, existing vertebral implant endplates suffer from several disadvantages. For example, existing vertebral implant endplates have bone contact surface designs which, due to local patient anatomies and angulations, may result in concentrating a large amount of force onto a small area on the prior art endplate bone contact surface. This is referred to as point-loading and may significantly increase the chances of adjacent vertebral body subsidence.
Further, existing vertebral implant endplates generally have a fixed angle relative to the implant body, and typically kits with several fixed-angle endplates are supplied to surgeons. Surgeons determine the appropriate combination of fixed-angle endplates according to patient anatomy during the procedure, which involves inserting a vertebral implant with a selected combination of endplates and taking an image of the spine. Inter-operative imaging allows the surgeon to verify the optimal spinal height and curvature is restored. If not, the vertebral implant is extracted, a different combination of fixed-angle endplates is selected and implanted with the vertebral implant, and the alignment verification step is repeated. This prolongs the surgical procedure, and in some cases may result in less than perfect match between the available fixed-angle endplates and local patient angulations and anatomy, which may lead to point-loading or may delay bone fusion, for example.